1. Field of the Invention
The present invention relates to an original scanning apparatus used with a copying machine, image reader and the like, and more particularly, it relates to an apparatus for scanning an original by shifting a reflection member with respect to a fixed original support plate and a fixed light source.
2. Related Background Art
Conventional slit exposure apparatus wherein an original support plate and a light source are fixed are already known, as disclosed in the Japanese Patent Laid-open Nos. 54-133140, 54-42129 and the like. FIGS. 18 and 19 show examples of conventional illuminating or lighting equipment.
The lighting equipment shown in FIG. 18 includes an elongated light source 101 disposed at one side of an original. The lighting equipment further includes reflection mirrors 102a, 102b for reflecting light from the elongated light source. The reference numeral 103 denotes an original support plate; 104 denotes an original; and 105 denotes a shiftable reflection member for optically scanning the original 104 by shifting the light from the reflection mirror 102b horizontally. On the other hand, the lighting equipment shown in FIG. 19 includes light sources disposed at both sides of an original. The same constructural elements as those shown in FIG. 18 are designated by the same reference numerals.
By the way, in the above-mentioned conventional lighting equipments, there arose a problem that the brightness on a peripheral portion of the original, particularly on a lateral edge portion of the original extending along the elongated light source was decreased as the shiftable reflection member was shifted away from the elongated light source because of the increased distance between the light source and a slit exposure scanning position.
FIG. 20 shows the distribution of the brightness on the original when the original is illuminated from one side thereof as in the equipment of FIG. 18, and FIG. 21 shows the distribution of the brightness on the original when the original is illuminated from both sides thereof as in the equipment of FIG. 19. In both cases, the distribution of the brightness is shows as the equi-illumination curves or lines. In FIGS. 20 and 21, arrows a and b show a condition that the light beams emitted laterally from the light source 101 escape outwardly from the surface of the original, and the thick arrow indicates a low illumination portion.
The reduction in the intensity of illumination as mentioned above causes the fog phenomenon in the outputted image from the copying machine and the like, thus worsening the ability to copy with high quality. Further, since the light source is fixed, the light source can more easily be arranged near the original support plate in comparison with the case where the light source is shiftable. However, when the light source is an elongated light source comprised of a plurality of illuminous bodies arranged in a line, the unevenness in the amount of light (intensity of illumination) is generated on the surface of the original in correspondence with the pitch between the adjacent luminous bodies, and, thus, it is impossible to uniformly illuminate the original along the longitudinal direction of the elongated light source.